Our overall objective is the understanding in molecular terms of the mechanism of protoplasmic streaming in the slime mold Physarum polycephalum. Our approach to this problem will be three-fold. First, we will continue our immunological studies on evolutionary changes in the structure of actin-like and myosin-like proteins looking for crossreactions using the micro-complement fixation technique. We will use the same immunological technique to detect changes in actin and myosin content in Physarum polycephalum during different stages of differentiation of the organism. Second, we will localize myosin and actin in the plasmodium of the organism in situ, using techniques to visualize antigen-antibody interaction at the ultrastructural level. Third, we will continue our studies on methods of purification of actin and myosin from Physarum with the hope of obtaining very high titer antiserum directed against these proteins.